Brightiness controls for electric lamps



J. w. STRANGE ETAL 2,4,54

BRIGHTNESS CONTROLS FOR ELECTRIC LAMPS Filed NOV. 14, 1950 '7Sheets-Sheet 1 20/4 208 20: 30p 20E- 20F 20's 20] 20H 20M 20w OWNWILLIAM STRANGE) JOHN SHAPLAND LOCKYER} raj ll'lve htor s.

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Aug. 19, 1958 J. w. STRANGE ETAL BRIGHTNESS CONTROLS FOR ELECTRIC LAMPSFiled Nov. 14, 1950 'T Sheets-Sheet 6 l/l/ lll/l/fil/ K! J)! Joe-mWILLIAM 'rfiAlvea mmmwm a 55 H K] In vewa r4. W Af'foi' h e Jaw SHAPLAWDLGCKYE Aug. 19, 1% J. w. STRANGE ETAL 2,848,654

BRIGHTNESS CONTROLS FOR ELECTRIC LAMPS 7 Sheets-Sheet '7 Filed Nov. 14,1950 HA WILLIAM STRANGE, H SHAPLAND O KYER;

2,4,fii Patented Aug. 19, 1958 BRIGHTNESS CONTROLS FUR ELECTRIC LAMPSJohn William Strange and John Shapland Loclryer, London, England,assignors to Thorn Electrical industries Limited, London, England, acompany of (Great Britain Application November 14, 1950, Serial No.195,508

2 Qlaims. (Cl. 315317) This invention relates to brightness controls forelectric lamps which may be low pressure discharge lamps-or incandescentfilament lamps.

A brightness control for low-pressure discharge lamps has been proposedwherein a hot-cathode, low-pressure electric discharge lamp, a ballastchoke and a variable impedance element are connected in series betweenthe terminals of a power source. A filament transformer has a primarywinding connected between the power source terminals and separatesecondary windings connected to supply heating current continuously tothe lamp electrodes whilst the lamp is in operation. The brightness ofthe lamp may be adjusted by varying the value of the variable impedanceelement.

Brightness controls for incandescent filament lamps are well known andusually consist of variable resistors connected in series with the lampor group of lamps to be controlled.

Such brightness controls can be used, for example, when the lamps areused for stage lighting. It is desirable to be able to adjust at willthe colour and the intensity of the light illuminating the stage. In onearrangement for obtaining colour variation a first series of lamps arecoloured red and connected to one brightness control, another series arecoloured blue and connected to a second brightness control, and theremaining lamps are coloured green and connected to a third brightnesscontrol, red, blue and green being primary colours. In a typicallighting plot the red control may be set to give full intensity, theblue to give half intensity and the green to give quarter intensity. Ifit is desired to alter the intensity of the lighting without anysubstantial change of colour the three controls must be operatedsimultaneously at rates such that the apparent brightness of the red,blue and green lamps is maintained approximately constant in the ratio 11 /2 1% respectively.

In one arrangement which has been proposed for use with incandescentfilament lamps, the three separate brightness controls are connected inseries with a master brightness control, and the master control alone isoperated when it is desired to alter the intensity of the lighting. Thismethod is not satisfactory and colour change cannot be avoided by itsuse since lamps of difli'erent colours do not change their apparentbrightness by the same amount for the same change in their operatingcurrent. Also the arrangement is not applicable to lowpressure dischargelamps.

An object of this invention is to provide-brightness control means whichenable the brightness of two or more lamps or series of lamps to bealtered substantially simultaneously and in some predetermined ratio toeach other.

According to this invention, a master brightness control for lampsincludes means adapted to displace the control members of secondarybrightness controls, each of which is adapted to be associated with alamp or series of lamps of a particular colour, substantiallysimultaneously from a position corresponding to zero brightness towardspredetermined positions at rates which are such functions of therequired distances of displacement of the control members of thesecondary brightness controls that the last-mentioned control membersall reach the said predetermined positions at substantially the sameinstant, and means enabling said predetermined positions to be alteredat will.

Embodiments of the invention will now be described, by way of example,with reference to the accompanying diagrammatic drawings wherein:

Fig. 1 is an elevational view of a first embodiment,

Fig. 1A is a schematic diagram of a variably tapped resistor for usewith the embodiment in Fig. 1,

Fig. 2 is an end elevation of the embodiment in Fig. 1,

Fig. 3 is a section taken along the line 3-3 in Fig. 1,

Fig. 4 is an elevational view of a second embodiment,-

Fig. 5 is a plan view of a part of the embodiment in Fig. 4,

Fig. 6 is an elevational view of a third embodiment,

Figs. 7 and 8 are sections taken along the lines 7-7 and 8-irespectively in Fig. 6,

Figs. 9, 10, 11 and 12 are sections taken along the lines 9-9, ltll.0,1ll-lll and l2-12 respectively in Fig. 7, and

Fig. 13 is a section taken along the line l3-l3 in Fig. 8.

In the first embodiment shown in Figs. 1 to 3 of the drawings, eachsecondary brightness control is a variablytapped resistor consisting ofa series of separate resistor elements 20A, 28B, 20C etc. connected to aseries of tapping contacts 21A, 21B, 210 etc. over which a controlcontact 22 slides. A master brightness control includes three parallelpanels 23 spaced from each other and fixed to a baseboard 24. The panelsare held rigidly apart by three screw bolts 25 fitted with six tubularspacing pieces 25A. The tapping contacts 21 consist of metal L-shapedpieces (see Fig. 3) inset into a rectangular bar 26 of insulatingmaterial, each bar 26 being held between two brackets 27 fixed to theadjacent panel 23 and each tapping contact 21 being provided with aterminal screw 28. Two pairs of brackets 29 are fixed to each panel 23and support two longitudinal parallel guides 30. A carriage 31 rides oneach guide 30, the two adjacent carriages being rigidly connected by atransverse yoke 32.

A control member in the form of a control contact 22 is formed by fiveresilient fingers fixed to their adjacent carriage 31 and insulatedtherefrom, the fingers being bent to engage the tapping contacts 21. Thecontrol contact is electrically connected to a terminal 22A by aflexible lead 22B. Each secondary brightness control includes an arm 34pivoted about a pin 35 which is fixed to its respective panel 23. Thethree arms of the master control are rigidly connected together at theirouter ends by a cr0ss-piece 36. The cross piece also serves as a supportfor the outer ends of three threaded rods 37, which are disposedparallel with and respectively close to the three arms 34. The rods arerotatably mounted in the inner ends of the arms 34 and in thecross-piece 36 and can each be rotated by means of an hand-wheel 33. Anut 39 is mounted on each rod 34 and is provided with a stud 40 engaginga longitudinal slot 41 in its respective transverse yoke 32. The nut 39is also provided with a pin 42 engaging a slot 43 in the arm 34 toprevent ro tation of the nut about the rod, thus rotation of the rod 37by means of its handwheel 38 causes movement of the nut 39 along the rodto any required position. It will be apparent that such movement of thenut 39 causes movement of the transverse yoke 32 longitudinally on itsguides 30. Also the arrangement is such that movement of each arm 34moves its associated transverse yoke 32 longitudinally on its guides andthus moves the control contact 22. The dimensions of the apparatus aremade such that, when the stud 40 is furthest from the pin 35,displacement of the arm 44 through approximately 60 moves the controlcontact 22 from an extreme position corresponding to zero brightness toanother extreme position corresponding to full brightness. The distancethrough which the control contact is displaced upon displacement of thearm 44 through approximately 60 can be adjusted by moving the nut 39,and thus the stud 46, along the arm.

Any number of secondary brightness controls can have their armsconnected to a common cross piece or to a suitable equivalent operatcrscontrol and thus be operated simultaneously. it will be understood thateach brightness control can be present e. g. while at the zerobrightness position, by rotating the respective handwheel 38 so as tomove its associated nut 39 to the required position on the rod 27. Thesecondary control members are moved simultaneously by movement of theoperators control (i. e. the cross-piece 26) and at rates which are sucha function of the respective distances of the nuts 29 from the pins 25that the control contacts 12 will all reach their intended operativepositions at the same instant, upon completion of the movement of thearm through approximately 60. The values of the separate resistorelements 10 are preferably made such that the ratio of the angularmovement of each arm 24 to the apparent brightness of the associatedlamp or lamps has a constant value. It is comparatively easy to design asingle continuously variable resistor element for use with incandescentfilament lamps and having the characteristic required to obtain the saidconstant ratio but it is more difiicult to design such a resistorelement for use with low-pressure discharge lamps owing to the muchwider range of resistance required and it is therefore preferable to useseparate resistor elements connected between tapping studs.

In the second embodiment shown in Figs. 4 and an arm 44 is mounted on ahorizontal shaft 45 carried by a bearing fixed to one corner of one oftwo end pieces 46 of a flat vertical contact assembly, which is in turnfixed to a baseboard 47. The two end pieces 46 are of insulatingmaterial and the arm 44 is fixed to the shaft 45 by a grub screw 44A.The contact assembly consists of alternate strips of metal 48A, 48B etc.and insulating material 49A, 493 etc. placed face to face and clampedtogether by two insulated bolts 5%. The edges of the metal strips areexposed on a vertical face and constitute the fixed contacts of avariably-tapped resistor, and separate resistor elements are connectedbetween each adjacent pair of strips by means of terminal screws 51. Astud 52 provided with a handle 53 of insulating material is slidable ina longitudinal slot 54 in the arm 434 and can be moved to any pointalong the arm. The stud acts as a tapping contact for the secondarybrightness control and is held in contact with one face of the con tactassembly by means of a spring washer 55 on the rod 45. The contactassembly is made sutficiently large to ensure that the stud remains incontact with the vertical face during movement of the arm. It isarranged that with the stud at its farthest position along the arm arotation of the shaft through approximately 60 will move the stud fromthe zero brightness position to the full brightness position. Any numberof arms, each associated with a separate contact assembly, may be fixedon the shaft 45 and operated simultaneously by a single operators mastercontrol, e. g. a handle 56 of insulating material which is fitted to oneof the arms As in the first embodiment the values of the separateresistor elements are preferably such that the ratio of movement of thearm/ apparent brightness of the associated lamp or lamps isapproximately constant. In use, the brightness controls are preset forthe desired value, in a similar manner to the first-mentionedembodiment, by moving the stud 52 by hand along the arm 44.

In the third embodiment shown in Figs. 6 to 13, as in the previous twoembodiments, each secondary brightness control is a variably tappedresistor. A master brightness control includes a casing 57 divided intothree compartments by two partitions 58, each compartment containing anarcuate rectangular section bar 59 which supports tapping contacts 60.Each tapping contact is provided with a terminal screw 61. The controlmembet for a secondary brightness control consists of a metal arm 62,mounted on a shaft 63 and capable of free rotation about the shaft. Thecontrol contact 64 consists of a carbon brush 65 mounted in the arm 61and springbiased into engagement with the tapping contacts 60, the armbeing provided at a point near to the shaft 63 with a terminal screw 66to which a flexible lead can be connected. The arm 62 terminates at itsfree end in a spigot 67 over which an operators handle 63 of insulat ingmaterial is fitted.

A collar 69 of insulating material is pinned to the arm and serves as ananchorage for a helical spring 70 which has its other end fastened to abracket 71 fixed to the casing 57. The helical spring biases acam-follower 72 on the arm into contact with one of a nest 73 of sixedge cams 74A, 748 etc. The nest 73 is mounted on a shaft 75, relativerotation of the shaft and the nest being prevented by a key 76, and ismovable axially along the shaft. The nest is moved by means of anoperators handle 77 rigidly connected to a yoke 78 which is pivoted onthe shaft and embraces the nest. A plate 79 connecting the yoke and thehandle 77 can be fitted into any one of six slots 80A, 80B, etc. in ablock 81, each slot corresponding to one of the six edge cams, which areset at different depths in the nest. The cam follower 72 is mounted inan insulating bush 32 (Fig. 12) which is in turn fitted in the arm 62,the cam follower "being thus insulated from the arm. The end of the camfollower which engages the edge cams is fitted with a roller 83.

The three nests 73 of the master control can be rotated simultaneouslythrough a maximum of about by an operators control handle 84 (Fig. 6)fixed to one end of the shaft 75. Each secondary brightness controlmember can be preset while at the Zero position by moving the nest 73until the plate 79 can be lowered into the slot 80 corresponding to thecam desired track 74. The control member can be preset while at aposition other than the zero position by moving the nest to the extremeleft, as seen in Fig. 6, to disengage the cam follower from the nest.Thereafter, the arm 62 is moved to the required position (e. g. that ofthe middle arm 62 in Fig. 6 which corresponds to half maximumbrightness) and the plate 79 is moved to the right until it can beengaged in the requisite slot 80, whereupon the cam follower is inengagement with the required cam track 74. In this embodiment the anglethrough which each arm 62 is rotated upon rotation of its associatednest through about 90 can be varied in five discrete steps between 0 andabout 60, rotation of the arm 62 through about 60 causing displacementof the control contact 64 from one extreme position corresponding tozero brightness to another corresponding to full brightness.

Any number of arms 62 and cam nests 73, etc. can be provided and thus beoperated simultaneously by a single operators master control e. g. thehandle 84.

As in the two previous embodiments the values of the separate resistorelements are preferably such that the ratio of displacement of the arm62/apparent brightness of the associated lamp or lamps is approximatelyconstant.

We claim:

1. A master brightness control for lamps including means adapted todisplace the control members of secondary brightness controls. each ofwhich is adapted to be associated with a lamp or series of lamps of aparticular colour substantially simultaneously from a positioncorresponding to zero brightness towards predetermined positions atrates which are such functions of the required distances of displacementof the control members of the secondary brightness controls that thelast-mentioned control members all reach the said predeterminedpositions at substantially the same instant, and means enabling saidpredetermined positions to be altered at will, wherein each controlmember includes a contact movable along a contact assembly upondisplacement of an arm, and means for displacing the arm constituted bya movably mounted nest of cams each of which cams is engageable with acam follower operatively connected to the arm simultaneously, andwherein the means enabling the said predetermined positions to bealtered at will are constituted by means for engaging the cam followerwith any selected cam of the nest.

2. A master brightness control for a group of lamps of different colors,including impedance means for fixing the current through each lampindependently to permit selection of a particular color mixture from thegroup of lamps of different colors; and means for varying all of saidimpedance means simultaneously and proportionately to reduce thebrightness of the light from the group while keeping the color mixtureconstant.

References Cited in the file of this patent UNITED STATES PATENTS1,194,451 Wiegand Aug. 15, 1916 1,759,903 Hunter May 27, 1930 1,955,906Crouse Apr. 24, 1934 2,192,673 Cooper Mar. 5, 1940 2,220,951 Borden Nov.12, 1940 FOREIGN PATENTS 389,889 Germany Feb. 15, 1924 679,393 GermanyAug. 4, 1939

